Without limiting the scope of the present invention, its background will be described with reference to isolating pressure between two regions in a well with a cement plug, as an example. Cement plugs are commonly set in a subterranean well at a desired location inside a casing string to isolate pressure between two regions in the well. In certain installations, this is accomplished by first, installing a bridge plug at the desired location in the casing string and then, lowered a dump bailer carrying a cement slurry into the casing on a conveyance such as a slickline, a wireline, a coiled tubing or the like. Once the dump bailer is positioned in the desired location proximate the bridge plug, the dump bailer is actuated to release the cement slurry. The cement slurry is deposited on a platform formed by the bridge plug and is supported by the bridge plug during curing.
In one type of dump bailer, gravity is used to shift a weight through the dump bailer to dispense the cement slurry from the dump bailer. It has been found, however, that such gravity operated dump bailers often fail to fully dispense the desired volume of the cement slurry from the dump bailer, which can result in cement slurry placement in undesired locations during retrieval of the dump bailer as well as additional trips into the well to add more cement. In another type of dump bailer, explosive components are used to generate pressure to dispense the cement slurry from the dump bailer. It has been found, however, that the use of explosive operated dump bailers can be undesirable due to safety concerns and their use may not be allowed in some jurisdiction due to local regulations. In a further type of dump bailer, a surface electrical power source is used to dispense the cement slurry from the dump bailer. It has been found, however, that the use of surface electrical power operated dump bailers can be undesirable due to the high deployment costs associated with the use of electric wireline packages.
Accordingly, a need has arisen for an improved dump bailer operable to release a cement slurry into a casing to isolate pressure between two regions in the well. A need has also arisen for such an improved dump bailer that does not solely rely on gravity to dispense the cement slurry. In addition, a need has arisen for such an improved dump bailer that does not require explosives to dispense the cement slurry. Further, a need has arisen for such an improved dump bailer that does not require a surface electrical power source to dispense the cement slurry.